Is it possible to restrict a .NET executable to a specific machine somehow so that it can only be run on that machine.
Yes, and I do that in my apps. It works wonderfully.
Getting the system info (CPUID, MacID, HDD details) is easy using WMI (highly recommended).
I created a system that's practically foolproof (unless you're a pro hacker).
When my apps are installed for the first time on the user's PC, they go back to my server using web services. They identify themselves using a password hash and look for an authorisation code/order id for the client.
If the client has the correct authorisation code the application encrypts and stores the system details on the client's computer and sends a hash of the info to my server where it is stored. The software is then activated on the client's computer using some hashed flags and every time the app is run the system info is compared with the hashed info in the files.
If the client re-formats the computer, all he needs is the order id to activate the software again automatically (when the program checks with my server, the system details are verified and approved if they match). If the client installs the software on another machine he must contact my support team to get approval.
-- All the information is encrypted and hashed (double encryption). -- All code is obfuscated and packed.
It's working pretty securely at the moment.
So yes, it's possible, it's been field tested and found working as well as any other protection system.